WIP: Ledger PKI feature

[srasoamiaramanana-ledger]

Description

This PR defines the command and syscalls to enable the Ledger PKI feature.

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.66%. Comparing base (c4b1de3) to head (663c173).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #599   +/-   ##
=======================================
  Coverage   59.66%   59.66%           
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  Files          12       12           
  Lines        1676     1676           
=======================================
  Hits         1000     1000           
  Misses        676      676           

Flag	Coverage Δ
unittests	59.66% <ø> (ø)

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